Power requirements for electron cyclotron current drive and ion cyclotron resonance heating for sawtooth control in ITER

13MW of electron cyclotron current drive (ECCD) power deposited inside the q = 1 surface is likely to reduce the sawtooth period in ITER baseline scenario below the level empirically predicted to trigger neo-classical tearing modes (NTMs). However, since the ECCD control scheme is solely predicated upon changing the local magnetic shear, it is prudent to plan to use a complementary scheme which directly decreases the potential energy of the kink mode in order to reduce the sawtooth period. In the event that the natural sawtooth period is longer than expected, due to enhanced alpha particle stabilisation for instance, this ancillary sawtooth control can be provided from > 10MW of ion cyclotron resonance heating (ICRH) power with a resonance just inside the q = 1 surface. Both ECCD and ICRH control schemes would benefit greatly from active feedback of the deposition with respect to the rational surface. If the q = 1 surface can be maintained closer to the magnetic axis, the efficacy of ECCD and ICRH schemes significantly increases, the negative effect on the fusion gain is reduced, and off-axis negative-ion neutral beam injection (NNBI) can also be considered for sawtooth control. Consequently, schemes to reduce the q = 1 radius are highly desirable, such as early heating to delay the current penetration and, of course, active sawtooth destabilisation to mediate small frequent sawteeth and retain a small q = 1 radius.Comment: 29 pages, 16 figure

Controllers for high-performance nuclear fusion plasmas

A succesful nuclear fusion reactor will confine plasma at hig temperatures and densities, with low thermal losses. The workhorse of the nuclear fusion community is the tokamak, a toroidal device in which plasmas are confined by poloidal and toroidal magnetic fields. Ideally, the confirming magnetic fields form a set of nested tori. A repetive magnetohydrodynamic (MHD) event in the plasma core (the sawteeth instability) perturbs the confirming magnetic field by producing seed islands. In low-pressure plasmas the seed islands will self-heal. In high-pressure plasmas the seed islands can grow and saturate. These neoclassical tearing models (NTMs) reduce the plasma performance or lead to plasma disruption. This sets the resistive pressure limit in tokamaks. High-performance operation in tokamaks therefore implies the control or amelioration of the NTMs. Controllers for the sawteeth and the NTMs will be discussed, with special emphasis on the development of dedicated sensors and models for MHD control

Real-Time Control of Sawteeth and NTMs in TCV and ITER

The main goal of this thesis is to demonstrate the capability of magneto-hydrodynamic (MHD) instability control, particularly sawteeth and neoclassical tearing modes (NTMs), in order to achieve high performance operation. Experiments and simulations have been carried out to pursue this purpose on different tokamaks: TCV (in Switzerland), KSTAR (in Korea), AUG (in Germany) and ITER (in construction in France). Each tokamak has different features such as machine size, heating systems, operation scenarios and energy confinement time scale, all the tokamaks are equipped or will be equipped with an electron cyclotron heating/current drive (ECH/ECCD) system for plasma heating/current drive and control of MHD instabilities. Therefore, this work focusses on the feasibility of using the localised ECH/ECCD beams to control the instabilities; sawteeth and NTMs. For the experimental part, sawtooth and NTM control experiments have been carried out. In TCV, novel ways of sawtooth period control - sawtooth pacing and locking - have experimentally been demonstrated using the TCV real-time control system. Based on the successful application of these methods to sawtooth control in TCV, we have next focussed on the extension of these new sawtooth period control methods to other tokamaks: KSTAR and AUG. In the 2013 KSTAR experimental campaign, the applicability of sawtooth locking using EC power modulation has been tested for sawtooth period control in the presence of fast particles generated by neutral beam injection (NBI). The KSTAR real-time control system was not ready for sawtooth pacing thus only locking has been examined. These preliminary KSTAR experimental results have shown the possibility of sawtooth period control using sawtooth locking, although proper locking was not obtained yet. The locking parameters would still need to be adjusted for single period locking to occur. In order for the investigation of the capability of sawtooth locking on KSTAR tokamak to be complete, more experiments with different locking parameters should be carried out. The sawtooth locking technique has also been applied to AUG plasmas. As in the KSTAR tokamak, the real-time control for sawtooth pacing was not available, thus sawtooth locking has been tested. The AUG plasmas were more complicated compared to TCV and KSTAR cases due to the fast particles effect on the evolution of sawtooth from both NBI and ion cyclotron heating (ICH). Sawteeth did not lock to the EC modulation in AUG experiments, though in some discharges they became somewhat more regular. However, the application of sawtooth locking to the AUG tokamak has been well initiated and more experiments will follow to understand better the behaviour of sawteeth and to determine the sawtooth locking range. In addition, sawtooth control was demonstrated and used in other experiments studying the role of sawteeth on impurity transport. Concerning the NTM control experiments, we have focussed on the enhancement of the NTM control strategy, which has been achieved in two ways. In previous TCV experiments, NTM stabilisation was obtained as ECH/ECCD deposition was swept in one direction until the mode disappeared. In order to ameliorate the control of NTMs, as a first improvement, a real-time version of the equilibrium reconstruction code LIUQE (RT-LIUQE) has been implemented in the TCV real-time control system. [...

Magnetic confinement experiments: plasma-material interactions, divertors, limiters, scrape-off layer (EX/D), stability (EX/S), wave-plasma interactions, current drive, heating, energetic particles (EX/W)

This paper summarizes the results presented at the 24th IAEA Fusion Energy Conference in the categories of plasma–material interactions, divertors, limiters, scrape-off layer (EX/D), stability (EX/S), wave–plasma interactions, current drive, heating, energetic particles (EX/W) in magnetic confinement experiments. In total, 149 papers including post-deadline papers have contributed to these categories. Several closely related papers, which are actually categorized in confinement (EX/C), have also been included. The understanding of experimental results has progressed remarkably, in particular, in the topics of resonant magnetic perturbation and ITER-like wall, which are the highlight of this conference. At the same time, identification of the bridging mechanism between the actuator and the consequence still requires further dedicated efforts so as to provide more accurate and reliable extrapolations to ITER and DEMO

原型炉のための技術基盤確立に向けた日本の取組

The establishment of technology bases required for the development of a fusion demonstration reactor (DEMO) has been discussed by a joint effort throughout the Japanese fusion community. The basic concept of DEMO premised for investigation has been identified and the structure of technological issues to ensure the feasibility of this DEMO concept has been examined. The Joint-Core Team, which was launched along with the request by the ministerial council, has compiled analyses in two reports to clarify technology which should be secured, maintained, and developed in Japan, to share the common targets among industry, government, and academia, and to activate actions under a framework for implementation throughout Japan. The reports have pointed out that DEMO should be aimed at steady power generation beyond several hundred thousand kilowatts, availability which must be extended to commercialization, and overall tritium breeding to fulfill self-sufficiency of fuels. The necessary technological activities, such as superconducting coils, blanket, divertor, and others, have been sorted out and arranged in the chart with the time line toward the decision on DEMO. Based upon these Joint-Core Team reports, related actions are emerging to deliberate the Japanese fusion roadmap